More than 100,000 people demonstrated against the TTIP and CETA trade accords in Berlin last October.
Photograph: Axel Schmidt/Getty Images

The controversial trade deal between Europe and the US has come under further fire after campaigners accused the government of blocking access to legal advice that shows its impact on the health service.

Campaigners warned on Tuesday that the legal documents could reveal the extent to which private health companies can sue the government using a secret tribunal system if a Whitehall policy change were to hit their profits.

As part of the Transatlantic Trade and Investment Partnership (TTIP), businesses can sue governments or public sector bodies for any loss of profits. The TTIP is an attempt by the US and EU to renegotiate thousands of trade tariffs and reduce the regulatory burden on exporters.

The business secretary, Sajid Javid, said in answer to a freedom of information request that disclosing the legal documents would make civil servants cautious when they “need space in which to seek candid advice from their lawyers”.

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Nick Dearden, the charity’s director, said: “If this trade deal is supposed to benefit all of us, why has it been so secretive? The documents we have seen so far have mostly come from Wikileaks or after intense pressure from campaign groups.

“After this move by the business secretary, the suspicion must be that it is a power grab by large companies keen to sweep away trade barriers and that the NHS is among the most vulnerable,” he said.

The EU Commission has denied shutting out stakeholders from the debate, arguing that it conducts regular meetings with interested groups and MEPs in the EU parliament.

Last year, Cecilia Malmström, the European commissioner for trade, proposed scrapping ISDS in favour of an international courts system after protests from several European governments.

A report by the business, innovation and skills select committee in the last parliament argued that ISDS was unnecessary and business disputes related to TTIP should be conducted through the existing legal systems of each nation.

It said the government must be allowed to expand the NHS without facing a legal challenge, and Brussels needed stronger evidence to back up its claim that the deal would bring a boost of £100bn a year to the UK.

It is understood that Barack Obama’s negotiating team has rejected Malmström’s reform proposal ahead of talks next month.